The invention relates to a feeding device according to the introductory part of claim 1.
Feeding mechanisms for supplying fasteners to inserting tools, like screwdrivers, are known in a great variety of types. They generally work with a stepping mechanism, by which fasteners, arranged at fixed intervals on a feed strip, are advanced into a position in which they are aligned with the tool and thus can be driven into the workpiece.
From U.S. Pat. No. 4,404,877 a power-driven screwdriver with a feeding device is known. The stepping mechanism here consists of an indexing lever, that is pivoted on a fulcrum. The pivoting of the indexing lever is governed by a pin, that is located at its after extremity, and is guided by a cam slot. The forward end of the lever carries, mounted pivotally, a feeding finger, that is under the bias of a spring. This feeding finger grips, during the swing of the lever, behind the next screw on the feed-strip, and advances this during the backswing of the lever to a position in front of a screw hole. The briefly described feeding mechanism contains all-together a number of interworking parts. It is thus costly to manufacture and is subject to breakdown.
Patent DE-PS 25 41 046 discloses a feeding device with a stepping mechanism in the form of a sprocket wheel, the teeth of which engage perforations in the margin of the feed strip. This sprocket wheel can be connected via a ratchet clutch with a stepping wheel. For this purpose there are recesses in both sprocket disks of the sprocket-wheel, and the mid-points of these recesses are arranged around the circumference of a circle. In the engaged position the projections, mounted on the stepping wheel, engage in these recesses. The stepping wheel is at this point subjected to the bias of a spring, which with the return motion of the slide element to starting position allows a temporary release of the connection.
U.S. Pat. No. 5,083,483 shows a feeding device for an inserting machine that is similar to the above-mentioned DE-PS 25 41 046, whereby a rocking lever is mounted on the slide element, and the sprocket wheel is pivotally mounted at the end of the rocking lever that is applied to the feed strip. The rotating action is achieved indirectly, through a ratchet wheel, which works in mesh with the sprocket wheel. At the other end of the lever a guide-pin is provided, which is movably mounted in a cam slot. Through the movement of the guide-pin as a result of an obliquely disposed portion of the cam slot, the ratchet wheel is moved downwards by the rocking lever and turns in a clockwise direction. The sprocket wheel, which is meshed with the ratchet wheel, is in this way rotated, so that the feed strip is made to advance by one lock-step.
Because of the ratchet coupling assembly, these known mechanisms are unduly costly to construct, and are also unavoidably prone to breakdown. In addition, the preparation of the feed strip must be very precise, since with these machines several teeth on the perimeter of the sprocket wheel are constantly meshed with the perforations in the feed strip. Finally, the radius of the feed strip in the contact zone of the sprocket wheel is relatively small, so that the strip is unduly stretched with the result that the interval between the successive perforations in the feed strip can vary in size. This failing also leads to interruptions in the operation of the machine.